In recent years, a vehicle such as an automobile is equipped with various in-vehicle devices, such as an audio device, an airconditioner, and a navigation device. Such in-vehicle devices have various complicated functions. For example, JP-A-2001-294101 discloses an input operation system to operate complicated in-vehicle devices. Specifically, the input operation system of JP-A-2001-294101 includes an operation panel on which a select switch group and a function switch group are located. The select switch group is operated for selecting an in-vehicle device to be used. The function switch group is assigned correspondingly to control contents of an in-vehicle device selected by using the select switch group. Thus, in-vehicle devices can be commonly operated by using the function switch group. The input operation system of JP-A-2001-294101 enables a user to operate various kinds of in-vehicle devices. Nevertheless, when a user operates such an input operation system, the user needs to find a switch device from many switch devices on the operation panel. Consequently, such an input operation system may not have a sufficient operability. In particular, when a driver performs a blind operation in a vehicle, it is hard to properly operate such an input operation system.
JP-A-2002-287950 discloses an input operation system including an operation device configured to accept user's operation in one of four directions in a cross form when a user selects a function to be used. In addition, the input operation system of JP-A-2002-287950 further includes a display device to indicate control contents corresponding to the four directions. In this case, indication regions of control contents are assigned to be in the cross form and indicated on the screen in consideration of user's operation in the cross direction. Therefore, a user can be easily understand correspondence between a control content and an operation direction in the cross form. However, in such an input operation system, indication regions of the control contents are small, since being assigned in a cross shape. Consequently, a content indicated in each indication region becomes small to result in spoiling its visibility.